[sdiy]Do you need to add more functions to your favorite LP4P VCF ?

[m.bareille at free.fr]

Hi Harry

> I don't know
> why anyone would ~not~ choose them for
> DIY or low volume apps (damn the extra
> cost - who cares ?)

Well my retailler have 405x in stock but not DGs. CMOS are simply more
popular... I guess the chip cost remain a real barrier for cheap commercial
devices , but i agree with you:  it is a chip who worth to be seen
more often into DIY schematics !


> The other point might be there will be
> phase shifts with different filter
> topologies... so a switch from a 4p
> to a 1 or 2p might well have a guaranteed
> 'pop'.

Exact ! I did not think to this at first time  :)


I think you might need to use
> separate recovery amps (15 different
> summing amps :^) and crossfade between the
> outputs to get true pop-free performance.

A kind of 16 channels Interpolating scanner with 15 summing amps !!! Arrrgghhh!
It is very heavy machinery for just a pop-free module !

>
> The A/D will be an issue with dithering
> between steps (will happen even using the
> high order bits only.  A workaround is to use
> a matching D/A converter (could be a very
> simple opamp summing network) and feed back
> a small amount (less than one bit you are using)
> into the input summer to create hysteresis. I've
> simulated this but have not built a live model.

Yes ! This was the pop's cause i suspected the most ...
The compensation method you suggest seem very interesting and new to me :)
I will take the time to try it even if i believe it won't be enough to remove
all switching noises  in the present case...


> The same issue is found on devices like the Wiard
> MiniWave... if you modulte with a slow input
> you can hear the dithering easily.

Interesting . I never had a MiniWave in hands, neither the schematic...and my
RAM wavetable module (frozen) project is not yet advanced enough to try this
kind of things on it: missing the fast ADC stage for the moment ...

Thanks for you precious advices :)

Cheers,

Marc B.




> >
> >
> >---- Original Message ----
> >From: m.bareille at free.fr
> >To: synth-diy at dropmix.xs4all.nl
> >Subject: RE: [sdiy]Do you need to add more functions to your favorite
> >LP4P VCF ?
> >Date: Mon, 29 Jan 2007 09:30:19 +0100
> >
> >>Hello,
> >>
> >>I have updated my site ...
> >>
> >>An answer to the topic's question is here proposed here :
> >>
> >>http://m.bareille.free.fr/modular1/vcf_multimode/extrapole.htm
> >>
> >>Have a nice day :!
> >>
> >>Cheers,
> >>
> >>Marc B.
>
>
>


nough